Ultrasonic distance scaling apparatus



Feb. 25, 1964 K. L. KING ULTRASONIC DISTANCE SCALING APPARATUS 2 Sheets-Sheet 1 Filed July 8, 1960 INV EN TOR.

MQMM

HTTPA/EY Feb. 25, 1964 K. L. KING uLTRAsoNIc DISTANCE scALING APPARATUS 2 Sheets-Sheet 2 Filed July 8, 1960 w mm WL. NA .im L MAM E (Y B H TTO/QA/E Y Uited States atent 3 121 955 ULTnAsoNrc nrsrmsicn scartato APPARATUS Kenneth L. King, Eastehester, NX., assgnor to United Aircraft Corptnatien9 East Hartford, Conn., a corporation of Deine/are Fitted .iuy 8, 19de, Ser. No. 41,616 1@ Ciaims. (Cl. 353-1) My invention relates to an ultrasonic distance scaling apparatus and more particularly to. an improved apparatus for translating linear motion to rotary motion.

In the prior art various forms of devices are employed to translate a linear movement into a rotational movement to achieve control. In the machine tool control art, for example, a lead screw or a mechanical rack and pinion are used to convert or translate a linear movement into a rotary movement. If these mechanical devices are to operate with any appreciable degree of accuracy, extremely precise gearing and very accurate machining and locating of parts is necessary. Electrical devices of a digital nature for translating linear movement into rotary movement involve the use of contacts which are subject to wear and which become dirty in use, thus requiring frequent cieaning and replacement after a relatively short period of time.

I lhave invented yan ultrasonic distance scaling apparatus for translating linear motion to rotational motion with a very high degree of accuracy. My apparatus does not require the precise gearing and very accurate machining and locating of parts which are required in mechanical devices of the prior art for translating linear motion to rotary motion. My apparatus does not involve the use of contacts with the result that it needs very little maintenance and has an extremely long life.

One object of my invention is to provide an ultrasonif` distance scaling apparatus for translating linear motion to rotational motion with a high degree of accuracy.

Another object of my invention is to provide ultrasonic `distance scaling apparatus which does not require the precise gearing or very accurate machining and loeating of parts required by mechanical distance scaling apparatus of the prior art.

A further object of my invention is to provide ultrasonic `distance scaling apparatus which requires little maintenance and which has an extremely long life.

Other and further objects of my invention will appear from the following description.

In general my invention contemplates the provision of a distance scaling apparatus in which i apply a signal to a length of solid material at a certain point whereby the signal is propagated down the length at the speed of sound in the material. A pickoif device produces an output signal in response to mechanical motion of the material at another point along its length. I provide means for measuring the time delay between the application of the signal and the arrival of the signal at the pickoflE point as `an indication of the physical distance between the point of application of the signal and the pickoif point. Preferably i measure the time deiay by determining the phase difference between a sinusoidal signal of fixed frequency and the delayed signal generated in the pickotf device. In one particular embodiment of my invention i apply to the length a modulated reference signal having a number of component :frequencies related by known factors. i separate the resulting pickoff signal into its component frequencies and determine the phase diderences between the respective reference signal and pickoif signal components to provide a very accurate measure of distance.

I may employ the distance indicating signal to control the position of the pick-off. provide my system with ice means for compensating for the effect of temperature change on the velocity of sound in the length of material.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIGURE 1 is a schematic view of my ultrasonic distance scaling apparatus with a block diagram illustrating the electrical circuit of my apparatus.

FIGURE 2 is a plot showing the relationship between the wave lengths of the vibrations of the scale member of my ultrasonic distance scaling apparatus and showing the change in phase difference between reference signals and magnetostriction voltage components along the length of the scale member.

FIGURE 3 is a perspective view of an alternate form of scale member which may be employed in my ultrasonic distance scaling apparatus.

Referring now to FIGURE l of the drawings my ultrasonic distance scaling apparatus includes a scale member it), 'which in the particular form of apparatus sho-wn in the figure is a thin-walled tube of a suitable ferromagnetic material such, for example, as nickel. As is known in the art the velocity of vibration propagation in a solid is expressed by the relationship V=E/P where E is Youngs modulus for the particular material and P is the density of the material. vFor a material such as nickel thisvelocity may be demonstrated to be y15,800 feet per second or approximately 190,00() inches per second.

Let us assume by way of example that a signal having a 19 kc. component is applied to the tube 10. A vibration of this frequency applied to the tube has a Wave length of 10 inches. AIn other words this vibration undergoes 360 of phase change in 10 inches along the length of the tube measured from the point of application of the vibrating force.

It is kno-wn that when a rod of ferromagnetic material is subjected to a longitudinal mechanical strain, its state of magnetization changes. Thus when the tube 10 is vibrated in the direction of its axis, the vibration is propagated down the tube 1d at the velocity of sound in the material of which the tube is formed. When the tube is formed of magnetostrictive material, an electromagnetic pickoff may be used. The voltage picked off at a point along the length of the rod is of the same frequency as the frequency of vibration. It will be evident, however, that the phase of the signal picked off at any point along the length of the rod diders from the phase of the signal producing the vibration by an amount which is proportional to the distance of the pick-off point from the point of application of the vibrating force.

I provide my apparatus with a transducer 12 adapted to be energized with an electrical signal for producing longitudinal vibrations in the rod 10. By way of example, assuming I desire control over a distance of 10 inches along the length of the lrod t1@ with a predetermined accuracy I excite the transducer `12, which may be a magnetostriction transducer or a barium titanate transducer, with a 1.9 mc. signal amplitude modulated with 190 kc. which in turn is amplitude modulated with 19 kc. The wave lengths of vibration components corresponding to these frequencies are respectively 0.1 inch, 1 inch and l() inches. To generate these frequencies and to apply them to the transducer 12, I couple the output signal of a 19 kc. oscillator 14 to a frequency multiplier 16 of any suitable type known to the art which produces an output signal having a frequency of l= kc. I apply the output signal of multiplier 16 to a second multiplier 18 which produces an output signal having a frequency of l.9 mc. I amplitude modulate the output of the 19 kc. oscillator 14 on the output of multiplier 16 by applying the output signals from the oscillator and the multiplier to a modulator Z of an appropriate type known to the art. I apply the output signal produced by modulator and the output signal of the multiplier I3 to a modulator 22 to produce an output signal which I apply to the transducer 12 through a channel 23. For purposes of clarity in exposition I have illustrated the upper half of the wave form on channel 23 in "FIGURE 2. I have correlated the wave form with a length of 10 inches along the tube 10 from the point at which the transducer 12 is connected to the tube. As can be seen by reference to FIG- URE 2, the vibration component resulting from the 19 kc. component of the signal on channel 2d, which I have represented by the wave lform A in FIGURE 2, goes through 360 of phase shift throughout the 10 inch length of the tube 10. The signal component having a frequency of 190 kc. represented by the curve B in FIGURE 2 goes through a complete cycle of phase shift in l inch along the length of the tube. The vibration corresponding to the 1.9 mc. component of the signal on channel 2li goes through 360 of phase change in one tenth of an inch along the length of the tube or cylinder 10. To avoid confusion I have shown only the portion of the 1.9 mc. component for the first two cycles of the 190 kc. component.

It will readily be appreciated by those skilled in the art that I may, if desired, successively divide a higher frequency signal such as 1.9 mc. to provide the lower frequencies of 190 kc. and 19 kc. The frequencies may be related by factors other than 10. To reduce the required bandwidth of the transducer 12, I have shown the amplitude modulation of the highest frequency by a lower frequency. Thus for the embodiment shown, transducer 12 must pass from 1.691 mc. to 2.109 me., thus requiring a bandwidth of only 21% approximately.

yReferring again to FIGURE 1, my apparatus includes a pick-off device, indicated generally by the reference character 2.4, which, as will be explained hereinafter, may be carried by the movable element such, for example, as a machine tool element (not shown) to be controlled. Where I desire to sense the mechanical vibration by the provision of magnetostriction material, the device 2d includes a toroidal coil 26 housed in a pair of ferrite cups 2S so constructed as to form a very narrow air gap 30- surrounding the tube 10. Owing to the magnetostriction effect, the mechanical vibration of the tube 10 produces a magnetic field in the ferromagnetic material. As a result the device 24 has induced therein an electrical signal containing all the component frequencies which are applied by the channel 24 to the transducer 12. I apply the signal induced in the pick-off device 24 to a demodulator 32 adapted to separate the '190 kc. wave from the signal. A channel 34 passes the output of the demodulator 32 to a second demodulator 36 which separates the 19 kc. wave from the demodulated 190 kc. ouput from the circuit 32.

Referring again to FIGURE 2 I have shown the variations in phase difference between the reference 19 kc., 190 kc., and 1.9 mc. signals and the corresponding components of the magnetostrictive voltage induced in the pick-off device 24 along the length of the tube 10 by the respective curves A', B', and C. To avoid confusion I have shown the phase difference curve corresponding to the frequency of 1.9 mc. only over the portion of the tube 10 from 3.0 inches to 5.0 inches.

In one application of my ultrasonic distance scaling apparatus I control the movement of a machine tool member or the like carrying the pick-olf 24. To accomplish this result, as is explained in detail hereinafter, I first shift the reference signals from the oscillator 14 and from the multipliers 16 and 1S through angles representing a certain position of the tool and then determine the phase difference between the shifted signals and the components of the magneto-striction signal induced in the device 2.4i. Referring again to FIGURE l, respective phase shifting networks 38, 40, and 4Z apply the outputs of the oscillator 14 and of the multipliers 16 and 18 to respective variable phase Shifters dei, 46, and 48. Each of the networks 3S, 40, and i2 shifts the signal applied thereto through 90 as is necessary for proper operation of t le phase difference detectors as will be explained hereinafter.

Each of the phase shifting networks d4, 415, and 48 is adapted to produce from 0 to 360 of phase shift in the signal input to the network. rhus network iii can produce an amount of phase shift representing ten inches of length along the cylinder 1.0, network 46 can produce a shift representing one inch along the length of tube 10 while the network 4S can produce an amount of phase shift representing one tenth of an inch along the length of a tube 10. I provide the respective shifting networks d4, 46, and 419 with manually operable knobs S0, 52, and 54 each of which is adapted to actuate its associated network through a respective linkage 5h. From the structure just described it will be seen that by setting the knobs 50, 52, and 5e, I can shift the reference signals to represent any particular distance along the length of the tube 10 up to ten inches from the point at which the transducer 12 is connected to the tube.

I cpply the respective outputs from the networks de, 26, and to phase difference detecting networks SS, 60, and 62. The output signal from the pick-off device 241 is applied directly to the phase detecting network d2 while the outputs of the respective demodulators 32. and 36 are applied to the phase difference detecting networks 60 and 58. It wiil be seen that the respective networks 53, 60, and 62 determine the phase differences between the respective reference signals and the components of the magnetostriction signal generated in the pick-off device 24. These phase difference detecting networks 53, 60, and 62 may oe of any suitable type known to the art. In one common type of phase dilierence detector, the signals are shifted relative to each other prior to their application to the detector for proper operation of the detector. It is for this reason that I pass the reference signals through the networks 3%, dit?, and 42 before their application to the shifting networks 44, d6, and 45. It will readily he appreciated that the system can be arranged to provide any arbitrary zero position offsetting the phase Shifters so that when control knobs 50, 52, and 54 read zero, one or more of phase Shifters ad, da, and i3 respectively are offset from their true zero phase shift position.

In operation of the phase difference detector 58 it produces an output signal which affords a measure of the diierence in phase between the phase shifted 19 kc. reference signal and the 19 kc. component of the magneto* striction signal induced in the pickoff device 24. This output of the detecting network 5% also is a measure of the difference between the actual position represented by the position of knob 50. Owing to the inherent limitations in the accuracy of the circuit components, this indication of deviations from desired position is relatively coarse. Phase detecting network e@ produces an output signal representing the difference in phase between the phase shifted kc. reference signal and the 190 kc. component of the magnetostriction signal induced in the pickof device 24. Since the 190 kc. vibration in the tube 10 passes through a complete cycle of phase change in l inch of length of the tube, the 190 kc. system has an accuracy of the order of 10 times the accuracy of the 19 kc. system. The phase detecting network 62 produces an output signal representative of the phase difference between the phase shifted 1.9 mc. reference signal and the 1.9 mc. component of the magnetostriction voltge in the pickoi'f coil 26. Owing to the fact that the 1.9 mc. vibration in the tube 10 passes through a complete cycle of phase change in one tenth of an inch of length along the tube 10, this 1.9 rnc. system is substantially ten times as accurate as is the 190 kc. system.

P.cspective channeis 64, e6, and di? apply the output orerror signals from the detectors S3, 6h, and 62 to a servomotor ampliier 7i) which supplies the excitation voltage for a servomotor 72. In response to signals from the amplier 70, the motor 72 drives the element such, for example, as a machine tool member to the position rep- Iresented by the settings of the knobs h, 52, and 54. When the pick-oil device 2d carried by the control element arrives at the position represented by the settings of the knobs Sil, 52, and 54, the respective phases of the components of the magnetostriction voltage induced in the pick-oil device 24 are the same as the phases of the shifted reference signals with the result that the outputs of all the pbase detectors 58, 60, and 62 are zero and the motor stops. We have indicated the connection between the motor 72 and the pick-oli device 214 schematically by the broken line 74 in FIGURE 1.

It will be appreciated that upon the occurrence o a change in temperature the velocity of sound along the tube changes. I provide my system with a means for compensating for such temperature change to prevent the change from adversely affecting the operation of my device. A bar 76 of a material such as Invar having a very low temperature coeicient of expansion connects a stationary pick-oft" device, indicated generally by the reference character 75, to the housing of the transducer l2. The length of the bar 76 is equal to that distance over which I desire control. In the particular example considered above, the pick-off device 78 is positioned at a distance of l() inches from the point at which the transducer I2 applies the vibrating force to the tube 1t).

I apply the magnetostriction signal induced in the device 7 8 to a demodulator Si) which operates to separate the 190 kc. component from the signal induced in the device 7d. I apply the output of demodulator 80 to one input terminal of a phase detector 82, the other input terminal of which is supplied with the 190 kc. reference through a channel 3l. I apply the magnetostriction signal induced in the device 78 directly to one terminal of a phase detector 84 which operates at 1.9 mc.; a channel 86 applies the 1.9 mc. reference signal to the other terminal of the phase detector 34. I apply the outputs from both the phase detectors 82 and 84 to the input terminals of an automatic frequency control circuit S8 of any suitable type known to the art. A channel 9h applies the output from the frequency control circuit S8 to the oscillator I4 to control the frequency of the latter.

It will be appreciated that with the pick-olf device '73 positioned at a distance of l0 inches from the point oi application of the vibrating force to the tube It), the phases of the components of the magnetostriction voltage induced in the pick-ofi device 7c will be precisely the same as those or" the reference signals with the result that the outputs of both phase detectors `Si?. and 84 are zero. Ii now a change in temperature occurs to produce a change in the velocity of sound travelling along the length of tube Ill, then the phases of the voltage components induced in the pick-ori device 7S are no longer the same as the phases of the reference signals. As a result of this condition the phase detectors S2 and @d produce outputs to cause the automatic frequency control circuit to change the frequency of the oscillator lid in such a direction as causes the phases of the reference to be equal to the `phases of the components of the magnetostriction voltage induced in the .pick-oit device 7d. It will be seen that =I employ only the two higher frequency components to compensate for the efect produced by a change in temperature. I have discovered that an appreciable change in temperature does not produce an error in the lowest frequency which is of a magnitude suhcient to affect the accuracy o` my apparatus to a signiiicant degree.

I apply a termination 92 to the end of the cylinder or tube lil remote from the transducer I2. rThis termination is formed of a suitable material such, for example, as a rubber compound which is molded on the end of the tube lil to prevent reiections `from the end of the tube. I so form this termination 92 as to provide a tapering contact with the end of the tube. As will be appreciated by those skilled in the art, the voltage standing wave ratios will then be substantially unity thereby eliminating the nodes of zero voltage when standing waves exist.

Itis essential for proper operation of my distance scaling apparatus that eddy currents generated in the magnetostrictive material making up the tube lll be held to as low a value as is possible. IFor this reason I form the tube l@ with an extremely thin wall and provide the tube with a slit ltltl extending in the direction of the tube length.

Referring now to FIGURE 3, in an alternate form of magnetos'triction member which may be employed in my distance scaling apparatus I coat a quartz trod 9d with a layer 96 of ferromagnetic material such, for example, as nickel. 'Ihc `layer 96 may be built up by any suitable method such, for example, as by electroplating. In this form of my invention the frequency or" the vibration is determined by the quartz and the layer 96 of nickel serves only to provide the magnetostriction electrical output. l@ne advantage of this form of my invention over that shown in FIGURE `l is that it is less affected by changes in temperature owing to the low temperature coefficient of expansion of quartz.

In operation of my ultrasonic distance scaling apparatus, I will assume that I wish to position a member such, for example, as a machine tool worktable at a particular location with respect to a reference point which is the point at which the vibrating force is applied to the tube itil. For example, I will assume that I wish to position the table at a distance of 2.879 inches from the reference point. To accomplish this result, I set the knob Si? at the 2.8 position; I set the knob 52 at the .87 position; and I set the knob 54- at the .O79 position. It will be noted that in each case I set the particular dial to a position corresponding not only to the digit in the place of signicance to which that dial corresponds but to a position which also includes the digit of most signiiicance in the next lo\l er order place of significance. This is necessary in order that ambiguities will be avoided which otherwise may occur as the system drives toward a null. That is, if a position of 5.75, for example, were commanded and the most signicant knob Sii Were set at 5.0 then the system might well drive toward the 4.75 position rather than the 5.75 position as desired.

With the particular dial settings outlined above, the 19 kc. indicator 5S produces an output signal representing the difference in phase between the phase shifted 19 kc. `reference signal and the 19 kc. component of the magnetostriction signal induced in the pick-oil device 24. This output signal represents the displacement of the worktable carrying the device 2d from the commanded 2.8 inch position represented by the setting of knob Sil. Under the influence ot this sig-nal, motor 72 drives the table and the device 2li toward the 2.8 inch position. The 190 kc. indicator di? produces an output signal representative ot the displacement of the table from the .8,7 position within the range ot positions from 2 inches to 3 inches as commanded by the setting of knob 52. Under the iniluence of this signal the servomotor 72 drives the table and the pick-oil device 2d toward the .87 position within the range of positions from 2. inches to 3 inches. The 1.9 mc. detector 62 produces an output signal which represents the displacement of the table and the pickofi device 24 from the .079 position within the range of positions from 2.8 inches to 2.9 inches. -Under the action of this signal, the servomotor '72 drives the table and the pick-oft device 24 until the table reaches the commanded 2.879 inch position from the reference position. lWhen the table arrives at this position, the outputs oi the phase detectors 5%, 6tlg and 62 all are Zero and the servomotor 72 is not energized.

Upon the occurrence of a change in temperature which results in a change lin the velocity of sound travelling along the length of the tube it) from the point at which the transducer l2 applies the vibrating force to the pickoff device 7S, the two phase detectors and produce output signals which actuate the automatic frequency control circuit to regulate the frequency of the oscillator ltd until the outputs from the detectors h2. and are zero. While l have shown and described a particular form of my ultrasonic distance scaling apparatus in which three frequencies and a tube length of lil inches are used, it will be seen that l may, if desired, use a tube of any length and l may employ more than three frequencies, if desired.

it will be seen that l have accomplished the objects of my invention. l have provided an ultrasonic distance scaling apparatus which converts linear displacement into rotary displacement without the use of mechanical parts which require accurate machining and location of parts. My apparatus employs no contacts and thus is not subject to the disadvantages such as dirt and wearing of systems which employ contacts. My apparatus provides an extremely rugged and reliable means for posi 'oning a controlled member such as a machine tool element with a high degree of accuracy.

llt will be understood that certain features and subconrbinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details Within the scope of my claims 'without departing from the spirit of my invention. it is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. Distance scaling apparatus including in combination a length of solid material, means for impressing a mechanical motion upon said length at a first point, the motion being propagated along the length at the speed of sound in said material, means positioned at a second point along the said length for detecting mechanical motion of said material at said second point, means responsive both to said detecting means and to said impressing means for producing an electrical signal as a function of the propagation time interval between the first point and said second point as an indication of the distance between the two points, a first channel coupling said impressing means to said material at said second point, means responsive both to said detecting means and to said impressing means for means for introducing a variable phase yshift into one of said channels.

2. Distance scaling apparatus including in combination a length of material, means adapted to be energized to vibrate said length at a rst point, a source of a reference signal of a fixed frequency, means for energizing said vibrating means from said source to propagate vibration alo-ng said length at the speed of sound in said material, means positioned at a second point along said length adapted to produce a signal in response to said vibration, means for shifting the phase of said reference signal, means for compa-ring said reference signal shifted in phase and said pick-off signal to produce an error signal as a function of the phase difference between said pick-oil signal and said reference signal shifted in phase and means responsive to said error signal for moving said pick-oli device to a position along said length to reduce said error signal to zero.

3. Distance rscaling apparatus including in combination a length of material, means adapted to be energized to vibrate said length at a rst point, a plurality of sources of reference signals having respective frequencies related by predetermined factors, means responsive to said sources for energizing said vibrating means to produce a vibration propagated along said length at the speed of sound in said material, a pic; oil positioned along said length at a second point and adapted to produce a signal in response to said vibration, means for resolving said pickoif signal into component signals corresponding to said respective frequencies and means for comparing said cornponent signals wit. said source signals of corresponding frequencies to determine the respective phase differences.

4.r -Distance scaling apparatus including in combination -a length of material, means adapted to be energized to vibrate said length at a `first point, a plurality of sources of reference signals having respective frequencies related by predetermined factors, means responsive to said sources for energizing said vibrating means to produce vibration propagated along said length at the speed of sound in said material, a pick off device positioned along said length at a second point and adapted to produce a signal in response to said vibration, means for resolving said pick-off signal into component signals corresponding to said respective frequencies, means for shifting the phase of said reference signals, means for comparing said component signals with the reference signals of corresponding frequencies shifted in phase to produce error signals proportional to the phase difference between the component signals and the respective reference signals of corresponding frequencies shifted in phase and means responsive to said error signals for moving said pick-off device to a position along said length to reduce said error sign-als to zero.

5. Distance scaling apparatus including in combination a length of material, means adapted to be energized to vibrate said llength of material at a iirst point, a source of a reference signal of a fixed frequency, means for energizing said vibrating means from said source to produce `a vibration propagated along said length at the speed of sound in said material, a pick-oil device positioned at a second point along said length and adapted to produce a signal in response to vibration, means for shifting the phase of said reference signal by an arnount representing a desired position of said pick-off device along said length, means for determining the phase difference between said phase shifted reference signal and said pick-oil signal to produce an error signal representing the displacement of said pick-ofi device from said desired position and means responsive to said error signal for moving said pick-oil device (to said desired position.

6. Distance scaling apparatus including in combination a length of material, means adapted to be energized to vibrate said length of material at a iirst point, a plurality of sources of reference signals having respective frequencies related by predetermined factors, means rcsponsive to said sources for energizing said vibrating means to produce a Vibration propagated along the said length 'at the speed of sound in said material, a pick-off device positioned at a second point along said length and adapted to produce a signal in response to said vibration, means for resolving said pick-off signal into component signals corresponding to said respective frequencies, means for shifting the phase of the respective reference signals by amounts corresponding to a desired position of said pick-off device, means for comparing said phaseshifted reference signals with said pick-oil component signals to produce error signals and means responsive to said error signals for driving said pick-oir` device to said desired position.

7. Distance scaling apparatus including in combination a length of material, means adapted to be energized to vibrate said length of material at a first point, a source of a reference signal of a certain frequency, means responsive to said source for energizing said vibrating means to produce a vibration propagated along said length at the speed of sound in said material, a pick-cti device positioned a second point along said length and adapted to produce a signal in response to said vibration, means for determining the phase difference between said reference signal and said pick-oil signal as a measure of the distance between said points, a stationary pick-off device positioned at a xed point along Said length to have a signa-1 produced therein and means responsive to said stationary pick-off signal for regulating the frequency of said reference signal.

8. In distance scaling apparatus having a length of material and ha'ving means for vibrating said length in rea sponse to a reference vsignal to produce a vibration propagated along said length at the speed of sound in said material, a temperature compensating arrangement including a stationary pick off Ipositioned at a predetermined point along said given length and adapted to produce a signal in response `to said vibration and means responsive to said pick-off signal for controlling the frequency of said reference signal.

9. Distance scaling apparatus including in combination a hollow tube of magnetostrictive material formed with a slit extending along its length, means adapted to be energized to vibrate said tube, a source of a reference signal of a lfixed frequency, means responsive to said source for energizing said vibrating means to produce a vibration propagated along said length at the speed of sound in said material, a pick-off device positioned at a second point 4along the length of said tube and adapted to produce a voltage in response to the magnetic eld generated by said vibration and means for determining the phase difference between said reference signal and said pick-oft signal.

10. Distance scaling apparatus including in combination a rod formed of a material having a low temperature coefficient of expansion, a layer of magnetostrictive material carried by said rod, means adapted to be energized to vibrate said rod, a source of a reference signal of a xed frequency, means responsive to said source for energizing said vibrating means to produce a vibration propagated -a'long said rod at the speed of sound in said rod material, a pick-off device positioned at a second point along the length of 'said rod and adapted to produce a signal in response to the magnetic eld generated by said vibration and means for determining the phase diference between said signals as a measure of the distance between said points,

References Cited in the le of this patent UNITED STATES PATENTS 2,394,455 Koch Feb. 5, 1946 2,401,094 Nicholson May 28, 1946 2,461,543 Gunn Feb. l5, 1949 2,542,627 Chevallier Feb. 20, 1951 2,612,772 iMcConnell Oct. 7, 1952 2,686,837 Sensiper .Tune 8, 1954 2,870,389 Fraser Jan. 2,0, 1959 2,907,939* Sant Angelo Oct. 6, 1959 2,947,929 Bower Aug. 2, 1960 2,956,344 Ran-tsch Oct. 18, 1960 2,985,018 Williams May 23, 1961 UNITED STATES PATENT oFTTcE CE TllTlCAlE @F CRECllN Patent No 3,12ly955 February 25, 1964 Kenneth L King lt is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 7,' lines 48 and 49 for "said material at said second point, means responsive both to, said detecting means and to said impressing means for" read --f= said signal producing means, a second channel coupling said detecting means to said signal producing means and No Signed and sealed this 30th day of June l964 (SEAL) Attest:

'.RNEST WQ SWIDER EDWARD J. BRENNER lfffstng Gi'faer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTIGN Patent No. 3, 121,955 February 25, 1964 Kenneth L., King 1t is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7,' lines 48 and 49, for "said material at said second point, means responsive both to said detecting means and to said impressing means for" read said signal producing means, a second channel coupling said detecting means to said signal producing means and r,

Signed and sealed this 30th day of June 1964 (SEAL) Attest:

'.RNEST We SWIDER EDWARD J. BRENNER uwstng Gi'fieer Commissioner of Patents 

4. DISTANCE SCALING APPARATUS INCLUDING IN COMBINATION A LENGTH OF MATERIAL, MEANS ADAPTED TO BE ENERGIZED TO VIBRATE SAID LENGTH AT A FIRST POINT, A PLURALITY OF SOURCES OF REFERENCE SIGNALS HAVING RESPECTIVE FREQUENCIES RELATED BY PREDETERMINED FACTORS, MEANS RESPONSIVE TO SAID SOURCES FOR ENERGIZING SAID VIBRATING MEANS TO PRODUCE VIBRATION PROPAGATED ALONG SAID LENGTH AT THE SPEED OF SOUND IN SAID MATERIAL, A PICK OFF DEVICE POSITIONED ALONG SAID LENGTH AT A SECOND POINT AND ADAPTED TO PRODUCE A SIGNAL IN RESPONSE TO SAID VIBRATION, MEANS FOR RESOLVING SAID PICK-OFF SIGNAL INTO COMPONENT SIGNALS CORRESPONDING TO SAID RESPECTIVE FREQUENCIES, MEANS FOR SHIFTING THE PHASE OF SAID REFERENCE SIGNALS, MEANS FOR COMPARING SAID COMPONENT SIGNALS WITH THE REFERENCE SIGNALS OF CORRESPONDING FREQUENCIES SHIFTED IN PHASE TO PRODUCE ERROR SIGNALS PROPORTIONAL TO THE PHASE DIFFERENCE BETWEEN THE COMPONENT SIGNALS AND THE RESPECTIVE REFERENCE SIGNALS OF CORRESPONDING FREQUENCIES SHIFTED IN PHASE AND MEANS 